Relay circuit



Oct. 13, 1936. I A. H. LAMB 2,057,384

RELAY C IRGUIT Filed July 7, 1952 3 Shee-tS-Sheet 1 aka 1, 16

Oct. 13, 1936. i AM 2,057,384

RELAY CIRCUIT Filed July 7, 1932 3 Sheets-Sheet 2 A. H. LAMB RELAYCIRCUIT Oct. 13, 1936.

Filed July '7, 1932 5 Sheets-Sheet 3 Patented a. 13, 1936 UNITED STATESPATENT OFFICE RELAY CIRCUIT Application July 7, 1932, Serial No. 621,32111 Claims. (Cl. 250-415) This invention relates to relay circuits andparticularly to control circuits of the type including electromagneticrelays.

Electromagnetic relays are open to the serious objection that unduefriction or a sticking of the switch contacts may prevent the armaturefrom moving. If the first surge of current does not develop a forcesufficient to overcome the resistance to movement, the continued flow ofcur- 'rent cannot develop any additional force to move the armature. Dueeither to this or other causes, relay circuits frequently fail tofunction properly and dangerous conditions may thereby be established.

The present invention will be described as applied to an automaticillumination control system, such as may be employed for turning on thesignal lights at a lighthouse when the normal or solar illuminationfalls, but it is to be understood that, in its broader aspects, theinvention may be embodied in other relay or control systerns.

An object of the invention is to provide improved relay control circuitsof the type employing electromagnetic relays. An object is to providecontrol circuits of the type stated and in which, if the relay fails torespond properly when the current flow to the solenoid is first startedor is stopped, current is intermittently applied to the solenoid torepeat the application of the force designed to actuate the relay, andthis cyclic operation is repeated until the relay does functionproperly. Another object of the invention is to provide a relay controlsystem in which the controlled or load circuit is normally energized orde-energized, according to the nature of the circuit and safetyrequirements, and an alternate condition can be established only whenthe relay system functions properly.

0 More specifically, an object is to provide an automatic control systemincluding a photoelectric device for opening or for closing a controlledcircuit under predetermined illumination conditions, and in which thenormal condition of the 5 controlled circuit may be altered onlywhen thepredetermined conditions obtain and the control system functionsproperly. A further specificobject of the invention is to provide anilluminatlon control system including signal lights that o are normallyenergized, and a photoelectric control effective to extinguish thelights only when the control functions properly and predeterminedillumination conditions obtain.

These and other objects and advantages of 55 the invention will beapparent from the following specification when taken with theaccompanying'. drawings, in which Fig. 1 is a circuit diagram of theinvention as embodied in an illumination control system in which thecontrolled circuit is normally energized;

Fig. 2 is a diagram of the same circuit but 11- lustrating the severalparts in the position which they occupy just after the controlledcircuit is opened; 9

Fig. 3 is a fragmentary circuit diagram of only those elements effectiveto insure opening of the controlled circuit;

Fig. 4 is a fragmentary diagram of an alternative arrangement forde-energizing the main relay; and

Figs. 5 and 6 show other circuits for changing the normal operatingconditions of the main or controlled circuit.

In the drawings, the reference character I identifies a photoelectriccell which is positioned to receive light from the sky or fromany othersource upon which the system of control is based. The photoelectric celldelivers current to the moving coil 2 of a sensitive relay 3 that has a25 contact, arm 4 cooperating with a lower contact 5 and an uppercontact I.

The main or power relay of the control system includes a solenoid l andan armature 8, the armature carrying or otherwise actuating the 30movable elements of a main switch 8 and auxiliary switches in and H.These elements are shown diagrammatically in the drawings and it E to beunderstood that the physical structure of the electromagnet and theswitches may'dif- 5' fer materially from the forms shown. The mainswitch 9 is included in the controlled circuit l2 and the auxiliaryswitches are in circuits of the relay system. As shown in Fig. 1, thecontrolled circuit I2 is normally energized, 1.49., the switch 0 9 isclosed, when current flow to the solenoid l is interrupted.

Low voltage current for operating the relay system may be obtained froman alternating current power line through a step-down transformer l3 anda full wave rectifier ll, a ballast lamp or resistance I! beingpreferably included in the secondary circuit. The transformer may be anordinary bell-ringing transformer of the type which draws substantiallyno current when the secondary circuit is open.

A lead It extends from the positive terminal ll of the rectifier bridgeII to the contact arm I of the sensitive relay 3, the contact I isconnected through switch H to the heater coil ll of a thermal switch,and the sensitive relay contact is connected directly to the heater coilII of a similar thermal switch. The heating circuits for the coils arecompleted through their respective movable arms 20. 2|, and a commonlead 22 to the negative terminal 23 of the rectiiier. The thermalswitches are preferably of the type in which the relatively stationarycontacts are carried on bimetallic strips 2|, 2!. respectively. tocompensate for the flexing of the bimetallic strips Ill, 2| which is dueto slow changes in the air temperature. For convenience of description.the thermal switch associated 'with the low current contact isidentified generically by reference character L, and the switchassociated with the high current contact I is identified as H.

The stationary contact of thermal switch L is connected, by a lead 26.to the lead II that runs to the positive terminal H of the rectifier,and a closing of switch L therefore short-circuits the rectifier throughleads II and 28, switch L and lead 22.

The solenoid 1 is connected to the positive side of the rectifier by alead 21 and the opposite terminal of the solenoid is joined, by lead 28,to the stationary contact of the switch H. The auxiliary switch III ofthe main relay is bridged across the leads 2! and 2!, i. e., closing ofswitch II connects the solenoid 1 directly across the rectifierterminals.

As shown in Fig. 2. the thermal switch H has been closed and the flow ofcurrent to solenoid I has lifted the armature l to open the main switch9 and to close the auxiliary switches It, I I. The successive stepswhich resulted in this operation are as follows.

The illumination at the light-sensitive cell I increased to such valuethat the increased flow of current through winding 2 moved the contactarm 4 into engagement with the high current contact 6, thus closing thecircuit to the heating coil is of switch K. This increased illuminationcontinued for such time, say one minute, that the bimetallic strip 2|flexed to engage its contact with that which carries by the "cold"bimetallic strip 25. The closing of switch H connected the solenoid Iacross the rectifier I4 and, with normal operation, this results in alifting of the armature to open switch 8 of the controlled circuit, andto close switches II and II.

With the closing of the holding switch III, the solenoid-rectifiercircuit is completed around the thermal switch H and therefore thecurrent will continue to flow to the solenoid even though theillumination at the cell I falls off and the contact arm I leaves thecontact 6, thus permitting the switch H to open. The contacts 5 and 8are preferably separated by a gap corresponding to a difference of, forexample, 5 foot-candles in the illumination at the cell I. Within thisrange of 5 foot-candles, the contact arm 4 does not engage eithercontact but, when the illumination falls below the lower critical value,contact arm I engages contact 5 and a heating circuit is completedthrough the coil II of switch L. If the condition of subnormaiillumination continues for a predetermined period, the switch L isclosed and the rectifier I4 is short-circuited. The armature drops down,closing the main switch 8 and opening the circuit to the heating coil IIat the switch II. The bimetallic strip II cools down after a shortinterval and the circuit elements again occupy the several positions asshown in Fig. l.

holding switch II.

In the event that the armature I fails to respond properly when thethermal switches L and H close, the current impulses to the solenoid Iwill be repeated until the armature does respond. With the circuit asshown in Fig. l, the open holding switch II prevents any change in themain relay until the contact arm I engages contact 8 for a periodsuilicient to effect closure of the switch H. If the armature I does notlift to open switch 9 when current flows to the solenoid I, the holdingswitch Ill does not close and therefore the solenoid I is connectedacross the rectifier in parallel with the heating coll I! of switch H,see Fig. 3. The resistances of coil II and solenoid I are so relatedthat the limited current output of the transformer II,and rectifier I4is not sufficient to maintain a current flow in coil I! which will holdswitch H in closed position. When the bimetallic strip 2| cools downunder the decreased current flow, the switch H opens and thereby breaksthe shunt circuit through the solenoid. The flow of current in coil I!increases and the switch H closes again to supply current to thesolenoid. Current surges are thus repeatedly supplied to solenoid l andany incipient welding of the contacts at switch 9 will eventually bebroken and the switch will open.

The intermittent application of a force to insure movement of thearmature when current flow to the solenoid is interrupted is due to theWith the main relay as shown in Fig. 2, the armature should drop toclose switch 8 and open switch II when switch L closes. If the armaturedoes not drop, the switch I I remains closed and therefore the heatingcircuit to coil II of switch L remainsclosed.

With switch L closed, no current flows in this heating circuit since therectifier is shorted by switch L. The bimetallic strip therefore coolsdown and switch L opens to permit current flow to solenoid I and also tothe heating coil, thus causing switch L to close a second time. Thisintermittent short circuiting of the rectifier continues until therepeated blows impressed on the armature 8 cause it to drop open,thereby opening the holding switch II.

As applied to the control of a danger or tramc light, such as alighthouse, it will be apparent that the invention provides for anextinction of the lights only when the illumination is above apredetermined critical value and the control system is functioningperfectly. This is due to the fact that the main switch 9 in thecontrolled circuit remains closed so long as power is not applied to thesolenoid I. A failure of the control system may result in an unnecessaryclosing of the main switch 9 but it cannot result in an opening of thesignal light circuit. Furthermore, an intermittent or chatteringoperation when the illumination approaches the critical control valuesis prevented by the delay action of the thermal switches L, H and therelatively wide separation of the contacts 5 and 6 of the sensitiverelay 3. Changes in illumination take place as a fluctuating or wavephenomenon, and not as a progressive increase or decrease in value. Byadjusting the relay contacts to close at a lower value of 5 foot-candlesand at an upper value of 10 foot-candles, and designing the switches L,H for approximately one minute of continuous heating to effect closure,l. have found that the main relay responds only to definite andrelatively permanent changes in the general illumination at the controlpoint, cell I.

S hown in the fragmentary circuit diagram,

Fig. 4, the thermal switch L may be arranged to short-circuit only onearm of the rectifier bridge l4 when the main relay, solenoid I andarmature I, is a direct current electromagnet. In this system, the lead28' extends from the stationary strip 24 of switch L to a bridgejunction adjacent the negative terminal Junction 23.

For some purposes, it is not necessary to provide a control based uponan upper and a lower critical value of illumination or of some othervariable factor. For such uses, the control system may be materiallysimplified. The relay circuit shown in Fig. 5 is adapted to close and toopen the main relay circuit as the illumination passes through a singlecritical value, but chattering of the main relay is prevented or reducedby including a thermal switch in the system. As many elements of thisrelay may be identical with some parts of the described circuit, theywill be identified by the reference numerals previously used. Thesensitive relay 3 has only one contact 6 for engagement by the contactarm 4, and this contact is connected to one terminal of the heating coilIQ of a thermal switch H. By employing an alternating currentelectromagnet, raw alternating current may be used in the heating andthe relay circuits. One terminal of the secondary of the transformer I3is connected to the contact arm 4 by a lead 30, and to the solenoid 'lby a lead 3|. The opposite terminal of the secondary is connected by alead 32 to the movable contact strip 2|, and the stationary contactstrip is connected to the solenoid. When the illumination at thephotoelectric cell reaches the critical value, the contacts 4, 6 engageand current fiows through the heating coil l9, thus closing switch H andpassing current to the solenoid 1 to raise the armature 8 and openswitch 9 in the controlled circuit l2. When the illumination falls belowthe critical value, the contacts 4, 6 open and the strip 2i cools downto open switch H, thus interrupting the current fiow to the main relay.

Another practical arrangement is to employ raw alternating current forthe heating circuit or circuits and rectified current in the main relaycircuit. Such a variation, as applied to the Fig. 5 circuit, isillustrated in Fig. 6. The heating circuit of the thermal switch H isthe sameas in the Fig. 5 circuit, and a rectifier I4 is interposedbetween the transformer l3 and the solenoid I. The solenoid 1 isconnected as one diagonal of the rectifier bridge I4 and the otherjunctions of the bridge are connected to the stationary contact strip 25and to one terminal of the transformer secondary. When contacts 4, 6engage, the heating circuit is connected across the secondary and, whenswitch H closes, the rectifier is connected across the transformer.

While the invention has been described as applied to an illuminationcontrol system, it will be apparent that certain features are equallyuseful in other control systems. So far as concerns the positiveoperation effected by the thermal switches of the Fig. 1 circuit, thephotoelectric cell may be replaced by other types of controlinstruments, or the cell and sensitive relay may be replaced bymanuallyoperated switches. For illumination control, safety requirementsare best satisfied by employing a normally closed illumination circuitbut, for other purposes, it may be desirable to employ a main relay inwhich the switch 9 opens when current flow to the solenoid I isinterrupted. The current for operating the system may, of course, bedirect current from batteries or a power source.

It will therefore be apparent that the invention is not limited to thespecific circuits herein illustrated and described since variouschanges, which will be obvious to those familiar with the design andconstruction of relay circuits, fall within the spirit of my inventionas set forth in the following claims.

I claim:

1. In a relay system, the combination with a main relay comprising asolenoid, an armature, a main and an auxiliary switch controlled by saidarmature, said auxiliary switch being closed when said armature is movedin response to current flow in said solenoid, and a source of current oflimited output, of a thermal switch including a heater .coil, means forclosing a circuit from said source fiirough said coil to close saidthermal switch, circuit elements for connecting said solenoid acrosssaid source and in parallel with said heater coil upon closure of saidthermal switch, and circuit elements including said auxiliary switch forcompleting said solenoid circuit independently of said thermal switchwhen the armature moves in response to current flow in said solenoidcircuit, the limited current output of said source being insuillcient tomaintain said thermal switch in closed position when said thermal switchis closed and said auxiliary switch is open.

2. In a relay system, the combination with a main relay comprising asolenoid, an armature, a main and an auxiliary switch controlled by saidarmature, said auxiliary switch having contacts which are closed whensaid armature is moved in response to current flow through saidsolenoid;

of a source of direct current, and energizing means for connecting saidsolenoid across said current source; and means including a thermalswitch for interrupting current flow through said main relay; saidinterrupting means comprising a circuit including in series the contactsof a primary control relay, said auxiliary switch, the heating coil ofsaid thermal. switch, and the said source of direct current.

3. A relay system as claimed in claim 2, wherein said current sourcecomprises a rectifier bridge having one pair of terminals for connectionto an alternating current power supply and a second pair of terminalsacross which a direct current voltage is developed by said rectifierbridge, said energizing means connects said main relay across saidsecond pair of terminals, and the contacts of said thermal switch arenormally open and are closed by current flow through said heating coilto short-circuit at least one arm of said rectifier bridge.

4. In a relay system, the combination with a main relay, a main switchoperated by said relay, and a source of alternating current, of a fullwave rectifier, a circuit for connecting the input terminals of saidrectifier across said alternating current source, a circuit forconnecting said main relay across the output terminals of saidrectifier, and control means operative to pass full-wave rectifiedcurrent to said main relay or alternaopening said switch, of aphoto-electric cell, a second relay actuated by current flow from saidcell, a transformer having a primary for connection to an alternatingcurrent source and a secondary, arectifier receiving alternating currentfrom said secondary, thermal switch means for completing a circuit toestablish a flow of rectified current from said rectifier to said mainrelay to energize the same, a second thermal means operative tointerrupt the flow of energizing current to said main relay, and meansincluding said second relay for controlling both or said thermal switchmeans.

6. In an illumination control system, the combination with a main relayhaving an armature, a source of alternating current, a rectifier, aphoto-electric cell, and a second relay controlled by the output of saidcell, said second relay hav ng a contact arm movable between a pair ofcon acts, of means operative repeatedly to energize and deenergize saidmain relay in the event that the armature or said main relay does notrespond substantially immediately to that condition of current flowthrough said main relay which is established by the engagement of thecontact arm of the second relay with one of the said contacts, saidmeans including a pair 01 thermal switches, means including said relaycontacts for completing heating circuits for the respective thermalswitches, circuit elements including said thermal switches foralternatively establishing and interrupting current flow through saidmain relay upon the closure of the respective thermal switches, andmeans including a pair of auxiliary switches actuated by the saidarmature for controlling current fiow in the respective heating circuits0! the said thermal switches.

7. An illumination control as claimed in claim 6, wherein saidalternating current source has a limited output or an order insufflcientto supply current for the simultaneous energization of one of saidheating circuits and said main relay,

and one of said auxiliary switches has contacts closed upon movement ofsaid armature in response to an energization of said main relay tocomplete an energization circuit for said main relay independent of thatthermal switch which closed to establish an initial current flow throughsaid main relay from said source and rectifier.

8. An illumination control as claimed in claim 6, wherein that one ofsaid thermal switches which interrupts current flow through said mainrelay has contacts for short-circuiting said rectifler, and the saidauxiliary switch which controls current flow in the heating circuit ofthat one thermal switch has contacts serially arranged in that heatingcircuit and closed by said armature when the latter is in its positioncorresponding to an energization of said main relay.

9. In a control system, the combination of a main switch having a directcurrent operating winding, a source of alternating current, rectifiermeans having input terminals for connection to said alternating currentsource, circuit elements for connecting said operating winding to theoutput terminals of said rectifier means, one c! said circuit elementsbeing switch means operable in one position to short-circuit saidrectifier to prevent the supply of rectified current to said operatingwinding, and means including an instrument-type relay for controllingthe operation of said switch means.

10. A control system as claimed in claim 9, wherein said rectifier meansis a full wave rectifier bridge, and said switch means is operable inone position thereof to short-circuit at least one arm of the saidrectifier bridge.

11. A control system as claimed in claim 9, wherein said rectifier meansis a full wave rectifier bridge, and said switch means is operable inone position thereof to short-circuit one set 01 terminals of the saidrectifier bridge.

ANTHONY H. LAMB.

